Adjustable construction preferably an article of furniture and a squeeze protection and a drive unit thereto

ABSTRACT

In adjustable structure with a drive unit ( 8 ), e.g., an actuator driven by an electric motor and controlled via a control unit, a jamming protection arrangement is needed in certain connections. A solution is provided to a jamming protection arrangement, based on a piezo element ( 20 ) incorporated in the structure, alternatively in the drive unit. The piezo element is connected with the control unit, which is constructed such that the drive unit is stopped or reversed if a deviation occurs in the force on the adjustable element ( 5 ) or the structure.

The present invention relates to a structure of the type defined in theintroductory portion of claim 1 and a jamming protection arrangement aswell as a drive unit therefor.

A widely used drive unit for performing adjustments is linear actuators,where an electric motor, via a gearing, drives a spindle having a nutmovable in the axial direction to which an activation element issecured, cf. e.g. EP 622 573 B1 to Linak A/S and WO 96/12123 to DietmarKoch (Okin). A particular form of linear actuators is lifting columnswhich are typically used for height-adjustable tables. The commerciallyavailable lifting columns are typically based on a spindle, but thereare also solutions with wire drives and endless chains, cf. e.g.PCT/DK02/00476 to Linak A/S. For the sake of completeness, it should bementioned that the drive unit may also be a rotary actuator, cf. e.g. WO01/17401 A1 to Unak A/S.

These actuators find general application, examples of use being foradjustable articles of furniture (e.g. chairs, beds, tables), hospitaland nursing equipment (e.g. hospital beds and sickbeds, patient lifters)and industrial equipment (e.g. agricultural machinery, conveyors,process systems, barrier and bar systems) just to mention a fewexamples.

Performance of an adjustment involves a risk of an object getting intothe path of movement of the element, or there might be something in thestructure itself that counteracts the movement. In this respect, adistinction is made here between a blocking protection arrangement whichis basically aimed at protecting the structure, and a jamming protectionarrangement which is basically aimed at protecting an object whichinadvertently enters the path of movement of the element. What is inmind here is primarily avoidance of injury to individuals.

For blocking protection, various solutions are known, such asoverloading couplings (U.S. Pat. No. 4,846,011), detection of anincrease in the motor current or detection of the speed of rotation ofeither the motor or of the gearing. In many cases the blockingprotection is also used in linear actuators, also as an end stop.Mention may here be made of a special structure where a contact arm actsagainst a spring force, cf. U.S. Pat. No. 4,307,799 to Andco ActuatorProducts and EP 727 601 to General Electric. The blocking protectionthus protects the structure against overloading, while the objectgetting jammed is exposed to the prescribed maximum load of thestructure.

As mentioned, the jamming protection is aimed at protecting the veryobject that gets jammed. An example of a jamming protection arrangementis provided in WO 01/117400 which relates to a rotary actuatorincorporated in a bed.

A particular problem is jamming protection in height-adjustable tableswhich must ideally be active both when the tabletop is lowered andraised. When the tabletop is raised, it may e.g. hit an adjacent table,a window frame or a shelf. Jamming protection is very importantparticularly when the table is present in a home with small children.

U.S. Pat. No. 5,495,811 discloses two different solutions, one where thetabletop is arranged loosely in a frame and rests on a contact. If thetabletop meets an obstacle in a downward direction, the tabletop islifted and the contact is activated to interrupt the current to themotor. Inexpediently, the tabletop rests with its entire weight and load(as a guideline 100 kg) on the object which has got jammed. The solutiondoes not either allow for the fact that the carrying frame hits anobstacle, nor is it active in the upward direction of the tabletopeither. The other solution is based on the so-called tape switches whichare adhered to the underside of the table. These are not active in theupward direction of the table either.

SE 516 479 C2 to Artektron AB discloses a solution based on a weighingcell in the form of a strain gauge arranged at the back of a U-shapedelement. The shown structure exclusively records deviations in themoment load on the tabletop. The drawing indicates a table of thegenerally used type having a leg at each end located rather close to therear edge of the tabletop. The front edge of the tabletop thus protrudesa considerable distance forwardly of the legs. This means that a minorchange of force at the front edge of the table results in a great changein the moment load, while even a rather great change of force in thearea of the leg is not recorded. The legs are typically connected withan architrave to achieve sufficient stability. If by accident a child,e.g. when playing, should get jammed between the architrave and thetabletop, this will not give rise to any special moment load with theconsequent risk that the jamming protection arrangement remainsinactive. A great vertical load directly on the strain gauge will notgive any signal at all, since this does not give rise to a moment load.From an overall point of view, the use of strain gauges involvescomplicated solutions and moreover has the drawback that they “drift”,i.e. they must constantly be calibrated somehow.

The object of the invention is to provide a jamming protectionarrangement which primarily offers a more complete protection, and issimpler and easier to incorporate than the previously known ones.

This is achieved according to the invention by a structure which ischaracterized by comprising a piezo element arranged in connection withone of the attachment points of the drive unit or in the drive unititself to record deviations in the force extending between theattachment points of the drive unit. Thus, the piezo element is not usedfor making absolute measurements, but exclusively for recordingdeviations on the basis of concrete situations. The absolute force to bemoved by the drive unit may basically be different from time to time,which is of minor importance. The essential point is that duringmovement the piezo element records deviations in the initial load toindicate that the adjustment element meets an obstacle and thenstops/reverses the motor. Limit values may be fixed as to how greatdeviations of the force may be tolerated before this is taken to meanthat the structure meets an obstacle.

In this connection it is particularly expedient that transient signalsfrom the piezo element are ignored or suppressed during starting of thedrive unit to eliminate the special forces that occur during start. Thismay be the transition from static to dynamic function, overcoming offorces of inertia, or a “binding”/“rooting” when the structure has beenat a standstill, and similar forces. Of course, the time of using thesignal from the piezo element may be adapted to the actual structure,force application and speed at which the drive units runs. It will beappreciated that the transient phenomenon is quite brief (typicallymilliseconds), so that in reality there will be no time for jamming tooccur.

In this connection it is noted that the controls are typically, but notexclusively microprocessor-based, thereby allowing desired threshold andlimit values to be incorporated in terms of software. In case ofcontrols not based on microprocessors, threshold and limit values may beprovided electronically.

In case of height-adjustable tables, e.g., the force may be varied byremoving or putting an object on the table. When the height of the tableis adjusted, the force may be different from time to time, which is ofminor importance. With the given initial load (force), the piezo elementwill exclusively record deviations in the force during the adjustmentitself, if the table top meets an obstacle in a downward or upwarddirection.

The solution of the invention is also independent on how the load isdistributed on the adjustable element, e.g. on a tabletop there aretypically local loads e.g. in the form of a computer, stacks of paper,etc. The essential point is exclusively the resulting force on the piezoelement.

The type of the piezo element is adapted to the structure concerned, butit has been found to be particularly expedient to use a passive soundgenerator containing a piezo element. These are generally known and arewidely used for emitting a brief sound, e.g. the well-known beep soundsin the operation of electronic apparatuses. The passive sound generatoris advantageous in that the piezo element is arranged on a thin,flexible disc of metal, so that a useful signal will be obtained evenwith the application of a relatively low force. Relative to a ceramicdisc or block-shaped piezo element which is to be specially designed forthe given purpose, the passive sound generator is a general andinexpensive component.

To avoid destruction of the piezo element by overloading, mechanicalstops may be incorporated in the structure which limit the travel of thepiezo element.

Further, the structure may be formed with a gearing so that just a minordirectly proportional part of the load is transferred to the piezoelement. Such a gearing might be sets of springs, where one set is incontact with the piezo element and has a spring constant smaller thanthe other set of springs between the stationary and movable parts of thestructure. It will be appreciated in this connection that the drive unitmay be associated fully or partly with the one or the other part.

The location of the piezo element(s) is adapted to the structureconcerned. In connection with the attachment of the drive unit, a piezoelement might be provided which recorded any change in the force on thedrive unit. In height-adjustable tables, a piezo element might bearranged below each leg. In tables having a cross member between thelegs, however, it should be positioned so as to allow avoidance ofjamming between the tabletop and the cross member. Expediently, thepressure transducer is arranged in the line of force between theattachment points of the drive unit, thereby achieving the most directimpact on the piezo element.

Particularly expediently, the piezo element is incorporated in the driveunit, viz. in connection with a force absorbing bearing in the actuator.Hereby, the drive unit may be supplied as a finished and thoroughlytested unit, which obviates separate subsequent mounting of the piezoelement in the structure and the consequent drawbacks.

How the braking is to take place may be adapted to the structureconcerned, just as it may be decided whether reversing of the drive unitis to be carried out. A simple and safe solution is short-circuiting ofthe motor windings. If rapid stopping of the drive unit is required, thecontrol may be adapted such that the rotation of the motor is turned soas to provide active braking. It may then be decided whether reversingproper of the drive unit is to take place. Also, a brake proper may beincorporated in the drive unit or overall in the structure, e.g. a typewhich is activated by a solenoid.

As stated in claim 20, the invention also relates to a jammingprotection arrangement as defined in claims 1–19 and constructed as aseparate unit, and, as stated in claim 21, the invention moreoverrelates to a drive unit with an incorporated or mounted jammingprotection unit as defined in claims 1–20.

An embodiment of the invention in the form of a height-adjustable tablewill be explained more fully below with reference to the accompanyingdrawing. In the drawing:

FIG. 1 shows a schematic view of a height-adjustable table, where thetabletop is shown transparent, and with the drive units shown separatein a retracted state,

FIG. 2 shows a drive unit In a fully extended state,

FIG. 3 shows a jamming protection unit with a piezo element mounted onthe outer end of the upper rod in the drive unit,

FIG. 4 shows an exploded view of the jamming protection unit with apiezo element shown in FIG. 2,

FIG. 5 shows a longitudinal section through a linear actuator,

FIG. 6 shows a cross-section through another embodiment of theinvention,

FIG. 7 shows a cross-section through an embodiment similar to the one ofFIG. 6, and

FIG. 8 shows a cross-section through a further embodiment of theinvention.

The desk shown in FIG. 1 comprises a lifting column 1 at each end. Thelifting column 1 consists of three mutually telescopic members 2 a, 2 b,2 c and are firmly mounted in a foot 3 with the lower end of the outermember 2 a, which is connected with a cross member 4 at the upper end.The tabletop 5 is mounted on the upper end of the inner member 2 c ofthe lifting columns.

The movement of the columns is caused by an incorporated drive unit 8,which is driven by an electric motor which is connected with a controlbox 6 with a power supply. The box also contains a control which isactivated by a control panel 7 arranged at the front edge of the table.The control may be based on rotary potentiometers, optical or magneticencoders for determining the height of the tabletop or purelyelectronically, as stated in WO 02/091539.

The drive unit 8 is of the type which is defined in the applicant'sinternational application PCT/DK02/00467, which is hereby incorporatedby reference in the present application.

The structure of the drive unit will now be described briefly for thesake of good order. It is based on a rod-shaped element 9 having a chainwhich extends around a gear wheel at each end. The one gear wheel isdriven via a gearing by a DC motor 10 secured to the end of the rod. Arod 13, 14 is secured to each chain run 11, 12 between the two gearwheels, said rod being secured to the outer member 2 a and to the innermember 2 c, respectively. When the motor is activated, the two rods 13,14 will synchronously extend the outer profile 2 a and the inner profile2 c relative to the intermediate profile 2 b as a consequence of themovement of the chain and correspondingly retract them when the rotationof the motor is turned. Reference is made to said internationalapplication for a more detailed explanation of the drive unit.

As will appear from FIGS. 3 and 4, the end of the rod 14 has mountedthereon a unit 15 containing a passive sound generator with a piezoelement. The unit comprises a substantially U-shaped frame 16 which fitsover the end of the rod 14 and is secured thereto with a pair of rivets1. A hous ing 19 having a cylindrical interior may be inserted into anopening 18 of the frame, and a capsule 20 resting on a flange 21 may beaccommodated in said housing. The capsule contains a passive soundgenerator in the form of a thin, circular, elastic metal plate on whicha piezo element is arranged, e.g. a kbs-20 db-4p. A pair of disc springs22 rest above the capsule 20. A screw spring 23 rests with one end onthe passive sound generator, said spring 23 extending through a circularrecess 24 at the top of the capsule 20 and further through a circularrecess 25 in the disc springs and provided at the other end with apressure shoe 26 having a short control pin, which extends into thespring, and the upper side of the head of the pressure shoe has anengagement bead which is received in a recess in the cover so that it isguided. A cover 27 is arranged on the disc springs 22 and the pressureshoe 26 of the screw spring, said cover being guided in a recess 28 atthe top of the housing 19 and with side edges on the upper side forguidance in the recess 18 in the frame 16. The cover 27 is kept inposition by a lid 29 which engages below an edge 32 on the housing 19with a pair of legs 30 terminating with flanges 31 facing toward eachother. The length of the legs 30 is adapted such that the lid 29 isallowed to travel. In a non-loaded state, the springs press the coverand thereby the lid 29 upwards, so that the lid grips the flanges 32 onthe housing with its edges 31. A U-shaped metal bracket 33 is secured inthe lid 29, having two upwardly extending legs for attachment to theinner member 2 c of the column. This takes place over an end plate bywhich the column is secured to the table top. The metal bracket thusreplaces the two flaps on the rod 14. The jamming protection as a unitmay thus be mounted readily on the drive unit without any modificationsto the mounting brackets being required. Thus, the drive unit with thejamming protection may thus be mounted selectively. Below the housing 19there is mounted a small printed circuit board 34 with terminals for theacoustic sound generator and connection to the control 6. As analternative to the metal bracket, the attachment may be performed with asmall guide pin on the lid and a screw, screw holes being indicated atthe side of the guide pin.

The spring constant of the screw spring 23 and the disc springs 22 isadapted so that just a small portion of the force is transferred to thescrew spring and thereby the acoustic sound generator.

The tabletop rests with its weight on the lid 29, which is carried abovethe cover 27 by the disc springs 22. It will be appreciated that thesesprings 22 are dimensioned to carry the weight of the tabletop and theload thereon. If the tabletop meets an obstacle during an upwardmovement, the force on the springs 22 will be increased, and the forceof the screw spring 23 on the acoustic sound generator will be increasedcorrespondingly, thereby signal ling the control 6 to change the forceon the tabletop. The control is adapted to stop the drive unit andreverse briefly for retraction (lowering) of the tabletop from theencountered obstacle. If during a lowering movement the tabletop meetsan obstacle, this will cause an initial relief, whereby the force of thescrew spring 23 on the passive sound generator is relieved, and a changein the force is recorded. The control 6 is then signalled to stop thedrive unit 8 and reverse briefly to raise the tabletop, therebyreleasing the object which got jammed. It will be appreciated that betabletop only affects the obstacle with a minor inconsiderable weight,i.e. the table-top will never hang on the obstacle with its full weight.

If the table should be overloaded with an extreme force, then themechanical brackets will prevent destruction of the passive soundgenerator. If the table is loaded strongly from above, the underside ofthe lid 29 will hit the upper side of the housing 19, and, conversely,if e.g. during moving and handling of the table a strong upwardlydirected force is unintentionally applied to the lower side of thetabletop or the legs are pulled, then the flanges 31 on the lid 29 willengage the edges 32 on the housing 19.

It will be appreciated that the invention may also be applied in anactuator of the type defined in the applicant's internationalapplication WO 02/29284, which is hereby incorporated by reference inthe present application.

With reference to FIG. 5, it will briefly be summarized that theactuator comprises a spindle 35 which is driven by a DC motor via a wormgear 36. The spindle has a nut 37 with an activation element in the formof an inner pipe 38 guided in an outer pipe 39. A compressive bearing40, in the present case a ball bearing, is arranged on the end of thespindle to absorb the compressive forces occurring on the actuator. Withsuitable modification, the jamming protection arrangement may bearranged immediately behind the compressive bearing, or in connectionwith the rear attachment 41 of the actuator, in the alternative at theouter end 42 of the inner pipe 38. The same, of course, applies toactuators which operate under tension, which merely differ by having atensile bearing instead of a compressive bearing.

As will appear, the invention provides a completely new path for theprovision of jamming protection in an adjustable structure or the driveunit which operates it.

FIGS. 6–8 of the drawing show a cross-section of three other embodimentsof the invention, and the same parts are designated by the samereference numerals as above. With respect to the embodiment in FIG. 6 itis noted that the passive sound generator comprises a disc 20 a with apiezo element resting on a disc-shaped spring element 20 b. The piezoelement is here affected directly by a pin 23 a on the lid 29. It isnoted that the pin may very well be formed with an outer spring-loaded,telescopic part so as to achieve a gearing, as described earlier. Thehousing is here secured to the stationary part of the structure and thelid with the pin to the movable element. The structure may be providedas a unit intended for incorporation, where the housing may e.g. bemounted in a support for a tabletop and the lid with the pin is securedto the lower side of the tabletop. The disc springs 23, here arrangedbetween two washers, carry the weight of the tabletop. In the embodimentshown in FIG. 7, the disc-shaped spring element with the piezo element20 a rests on a corrugated disc 20 c. Connection wires to the piezoelement and the pin are indicated at 43 a, 43 b. The housing which iscircular here, has an annular flange 32 which cooperates with a flange31 a on a surrounding ring 30 a. This ring 30 a is provided with screwholes for attachment of the ring to the movable part. Here, the lid 29may be secured to the stationary part by a downwardly extending pin 44.The embodiment shown in FIG. 8 differs in that the piezo element 20 d isa ring mounted between two discs 45. There is an air gap between asurrounding ring 46 and a disc 47. The pressure from the two discsprings 22 will propagate through the intermediate discs to the piezoelement 20 d.

Disc springs are used in the stated examples, but nothing prevents theuse of screw springs, but the disc springs are more suitable in thepresent examples.

Finally, it should be noted that the jamming protection has no directrelation to end stops in actuators or their quick release function (EP577 541 B1 to Linak A/S). These functions may occur concurrently withthe jamming protection.

1. An adjustable structure, comprising: a stationary part (1, 3), anadjustable element (5) connected therewith, a drive unit (8) for causingadjustment of the element (5), said drive unit (8) with a movableactivation element (14; 38) and another part (13: 41) being secured tothe adjustable element and to the stationary part, respectively, saiddrive unit comprising an electric motor (10) for the driving thereof, acontrol unit (6) for controlling the drive unit, a sensor (15) connectedto the control to currently record deviations in the load on theadjustable element in operation and, in response to this, to signal thecontrol unit to stop/reverse the motor, and wherein the sensor is formedby a piezo element (20) arranged in connection with one of theattachment points of the drive unit (8) or in the drive unit itself torecord deviations in the force extending between the attachment pointsof the drive unit.
 2. A structure according to claim 1, wherein thesignals from the piezo element are ignored during the start of the driveunit.
 3. A structure according to claim 1, wherein the signals from thepiezo element are used only when these have found a constant level afterthe start of the drive unit.
 4. A structure according to claim 1,wherein the piezo element is positioned at a location in the line offorce between the attachment points of the drive unit.
 5. A structureaccording to claim 1, wherein the piezo element is arranged inconnection with a force absorbing bearing (40) in the drive unit.
 6. Astructure according to claim 1, comprising a passive sound generator(20) containing a piezo element as a sensor.
 7. A structure according toclaim 1, comprising mechanical stops (31, 32; 29, 19) which limit travelof the piezo element.
 8. A structure according to claim 1, comprisinggearing so that just a minor directly proportional part of the force istransferred to the piezo element.
 9. A structure according to claim 8,wherein the gearing comprises a set of springs, where one spring (23) isin contact with the piezo element and has a spring constant smaller thananother spring (22) between the stationary and movable parts of thestructure.
 10. A structure according to claim 8, the spring (22) isformed by disc springs, while the spring (23) is formed by a screwspring.
 11. A structure according to claim 9 wherein the spring (22) isdimensioned to carry the weight of the movable part and the maximumweight which the part is intended to be capable of carrying.
 12. Astructure according to claim 10, wherein a jamming protectionarrangement is provided as a unit comprising a housing (19) whichaccommodates the piezo element (20).
 13. A structure according to claim12, wherein the housing (19) comprises a lid (29) with legs (30) formedwith abutments (31) for cooperation with abutments (31) on the housingto limit travel of the lid.
 14. A structure according to claim 13,wherein the springs (22, 23) are accommodated in the housing, and atthat the spring (22) pushes the lid (29) away from the housing.
 15. Astructure according to claim 12, wherein the jamming protectionarrangement comprises a frame (16) for the housing (19).
 16. A structureaccording to claim 15, wherein the housing (19) is received in a recess(18) in the frame.
 17. A structure according to claim 12, wherein thejamming protection arrangement comprises a printed circuit board (34)for the connection of the piezo element and for the connection of thecontrol (6).
 18. A structure according to claim 12, wherein the jammingprotection arrangement is provided with mounting brackets for themounting of the movable element (15).
 19. A structure according to claim12, wherein the jamming protection arrangement is mounted on the end ofthe activation element (14; 38) of the drive unit.
 20. A jammingprotection arrangement as defined in claim 12, configured as anindependent unit.
 21. A drive unit having an incorporated or mountedjamming protection arrangement as defined in claim 12.